PROVINCETOWN — Lobster boat captain Beau Gribbin watched from three-quarters of a mile away as the Twin Lights appeared to catch on something underwater as it dredged for scallops late Sunday morning.

The Glutton, piloted by Gribbin, and the 40-foot Twin Lights, piloted by Jean Frottier, both out of Provincetown, had fished alongside each other for 10 years. The two fishing crews were in their usual spot: an area of state waters two miles north of Provincetown that draws both lobster and scallop fishermen.

There were unusually high seas Sunday, because of recent storms, Gribbin said Tuesday. His vessel hauled eastward, which gave his crew a good view of the goings-on of the fiberglass-hulled Twin Lights.

Frottier turned the Twin Lights down wind for calmer seas, which is customary when there's entanglement, Gribbin said. Then the Twin Lights appeared to take on water and lean sideways, and Gribbin put his binoculars up.

"We saw him roll over," Gribbin said. "He just rolled right over."

The one crew member on the Twin Lights, Eric Rego, was rescued by the crew of the Glutton.

Frottier, 69, of Wellfleet is believed to have died aboard the Twin Lights, although there has been no official confirmation yet. An attempt to reach the Frottier family on Tuesday was unsuccessful.

On Tuesday, the Coast Guard made plans to use a remotely operated vehicle, or ROV, to get a closer look at the Twin Lights, which sits on the ocean floor in 198 feet of water. The life raft from the Twin Lights washed up Tuesday on the shore of the Cape Cod National Seashore, along with fishing totes, baskets and line, Coast Guard Station Provincetown Chief John Harker said.

The Coast Guard has opened an investigation, Coast Guard spokesman Senior Chief Jamey Kinney said Tuesday. Investigations of this sort can take months, he said.

The ROV, which will likely be equipped with still and videocameras among other equipment, will allow state police divers and the Coast Guard to determine the status of the Twin Lights, its position in the water and if there is a body on board, Harker said. The schedule for the ROV is still being determined, and will depend on the weather, the agency loaning the ROV and other factors.

"It's in the planning stages," Harker said. "The current is some of the worst in the Northeast, and when you add 200 feet for diving, it's a very technical operation."

On Sunday, Gribbin watched the vessel overturn, called the Coast Guard, cut the fishing lines his crew was working on and steamed eastward to the disabled Twin Lights.

The vessel disappeared within what seemed like a couple of minutes and then bobbed back up to the surface with just the bow sticking out, Gribbin said. That's when his crew realized that the Twin Lights "was going to go down." They saw Rego clinging to the side of the boat.

"He was pretty beat up," Gribbin said.

The crew of the Glutton pulled Rego aboard, and he told them that Frottier was most likely trapped in the pilot house. They hoped then that Frottier would come swimming out of the boat, given his decades of commercial diving experience, or that he'd found a pocket of air in the bow. One crew member, who is also a good friend of Frottier, donned a diver's suit, went in the water and swam over to the bow of the Twin Lights. The diver banged on the bow, hoping for a response.

"He beat on the hull," Gribbin said. "He laid his head to the hull. There was no response."

The question then was what to do, Gribbin said, given the seas, the strong currents, the precariousness of the vessel and the potential of a 40-ton vessel sinking. Gribbin decided not to risk any more lives.

"You would be putting yourself in harm's way," he said.

His crew and other lobster boat crews in the area, some from Plymouth, ran a search pattern in the waters around the Twin Lights until sunset. By that time, Air Station Cape Cod had sent a helicopter and a Falcon jet, and two Coast Guard cutters and state police divers helped with the search as well.

Rego, who had been in the 49-degree waters for a little under 10 minutes, was "borderline hypothermic" but declined to be immediately taken to land by the Coast Guard, Gribbin said. Instead, Rego took a hot shower aboard the Glutton, put on dry clothes and stayed with that vessel as the crew helped search for Frottier.

"I'm glad I was there," Gribbin said. "But I wouldn't wish that on too many people. It was a hard thing. It's really hard on his family."

On Monday, the crew of the Glutton returned to the area to search again, Gribbin said. "You're still hoping for that miracle."